Grit Chamber

Purpose: The purpose of the grit chamber is to renew grit from the wastewater by settling.

Description: The grit chamber is a cylinder shaped concrete basin that allows the flow velocity to slow to the point that the relatively large inert grit particles will settle out while the lighter biodegradable organic materials pass through to the secondary treatment process. Flow enters the grit basin at a tangent to the circular side. This induces a vortex flow pattern in the chamber, which improves the efficiency of grit removal. A four bladed paddle is suspended in the chamber and operates to enhance the vortex action. The paddle is driven by an electric motor through a constant speed gear reduction unit. The net effect is that the amount of organic material settled out with the grit is minimized. The settled grit collects in a cylindrical sump below the center of the main grit chamber. The accumulated grit is removed by pumping. A non potable water (NPW) line extends into the grit sump to agitate and resuspend settled grit before and during grit pump operation. Flow of the NPW is regulated by an electric solenoid valve that is interlocked with the grit pump so that the valve opens to start agitation of the settled grit before the pump starts.